Delete unnecessary nil checks from entry

entry.go

@@ -43,6 +43,16 @@ func (e *Entry) checkAuthors() error {
 	return nil
 }
 
+func alternateRelExists(l []*Link) bool {
+	for _, link := range l {
+		if link.Rel == "alternate" {
+			return true
+		}
+	}
+
+	return false
+}
+
 func (e *Entry) AddExtension(name string, value any) {
 	e.Extensions = append(e.Extensions, &ExtensionElement{XMLName: xml.Name{Local: name}, Value: value})
 }
@@ -60,35 +70,33 @@ func (e *Entry) Check() error {
 		return fmt.Errorf("entry %v: %v", e.ID.URI, err)
 	}
 
-	if e.Categories != nil {
 	for i, c := range e.Categories {
 		if err := c.Check(); err != nil {
 			return fmt.Errorf("category element %v of entry %v: %v", i, e.ID.URI, err)
 		}
 	}
-	}
 
 	if e.Content != nil {
 		if err := (*e.Content).Check(); err != nil {
 			return fmt.Errorf("content element of entry %v: %v", e.ID.URI, err)
 		}
+	} else {
+		if !alternateRelExists(e.Links) {
+			return errors.New("no content element of entry %v and no link element with rel \"alternate\"")
+		}
 	}
 
-	if e.Contributors != nil {
 	for i, c := range e.Contributors {
 		if err := c.Check(); err != nil {
 			return fmt.Errorf("contributor element %v of entry %v: %v", i, e.ID.URI, err)
 		}
 	}
-	}
 
-	if e.Links != nil {
 	for i, l := range e.Links {
 		if err := l.Check(); err != nil {
 			return fmt.Errorf("link element %v of entry %v: %v", i, e.ID.URI, err)
 		}
 	}
-	}
 
 	if e.Published != nil {
 		if err := e.Published.Check(); err != nil {
@@ -130,13 +138,11 @@ func (e *Entry) Check() error {
 		}
 	}
 
-	if e.Extensions != nil {
 	for i, x := range e.Extensions {
 		if err := x.Check(); err != nil {
 			return fmt.Errorf("extension element %v of entry %v: %v", i, e.ID.URI, err)
 		}
 	}
-	}
 
 	return nil
 }

feed.go

@@ -156,21 +156,17 @@ func (f *Feed) Check() error {
 		}
 	}
 
-	if f.Categories != nil {
 	for i, c := range f.Categories {
 		if err := c.Check(); err != nil {
 			return fmt.Errorf("category element %v of feed %v: %v", i, f.ID.URI, err)
 		}
 	}
-	}
 
-	if f.Contributors != nil {
 	for i, c := range f.Contributors {
 		if err := c.Check(); err != nil {
 			return fmt.Errorf("contributor element %v of feed %v: %v", i, f.ID.URI, err)
 		}
 	}
-	}
 
 	if f.Generator != nil {
 		if err := f.Generator.Check(); err != nil {
@@ -184,13 +180,11 @@ func (f *Feed) Check() error {
 		}
 	}
 
-	if f.Links != nil {
 	for i, l := range f.Links {
 		if err := l.Check(); err != nil {
 			return fmt.Errorf("link element %v of feed %v: %v", i, f.ID.URI, err)
 		}
 	}
-	}
 	if hasAlternateDuplicateLinks(f.Links) {
 		return errors.New("links with with a rel attribute value of \"alternate\" and duplicate type and hreflang attribute values found")
 	}
@@ -229,21 +223,17 @@ func (f *Feed) Check() error {
 		}
 	}
 
-	if f.Extensions != nil {
 	for i, x := range f.Extensions {
 		if err := x.Check(); err != nil {
 			return fmt.Errorf("extension element %v of feed %v: %v", i, f.ID.URI, err)
 		}
 	}
-	}
 
-	if f.Entries != nil {
 	for i, n := range f.Entries {
 		if err := n.Check(); err != nil {
 			return fmt.Errorf("entry element %v of feed %v: %v", i, f.ID.URI, err)
 		}
 	}
-	}
 
 	return nil
 }